Marine biologists are scratching their heads over the spate of shark attacks near Egypt’s Red Sea port of Sharm El-Sheikh, the BBC reports. The waters near the city, which are popular for swimmers, snorkelers, and scuba divers, have seen attacks that have left one tourist dead and four injured in the past week.

The attacks started last week when a shark bit three tourists in a single day. Since then another swimmer has been injured and last Sunday a German woman was killed very close to the shore. Most of the beaches are now closed and authorities are warning people to swim in groups and avoid swimming at night.

The attacks were carried out by more than one shark from more than one species, including an oceanic whitetip and a mako. Marine biologists say this is “highly unusual”. They’re unsure what has caused the attacks, but suspect that when a cargo ship dumped a load of animal carcasses overboard near the shore it might convinced the sharks that it was a new feeding ground.

The mako has since been caught, but the oceanic whitetip, which is believed to have killed the German woman, is still at large.